From 2ff396be602f10b5eab8e73b24f20348fa2de159 Mon Sep 17 00:00:00 2001 From: Jeff Moyer Date: Tue, 2 Sep 2014 13:17:00 -0400 Subject: aio: add missing smp_rmb() in read_events_ring We ran into a case on ppc64 running mariadb where io_getevents would return zeroed out I/O events. After adding instrumentation, it became clear that there was some missing synchronization between reading the tail pointer and the events themselves. This small patch fixes the problem in testing. Thanks to Zach for helping to look into this, and suggesting the fix. Signed-off-by: Jeff Moyer Signed-off-by: Benjamin LaHaise Cc: stable@vger.kernel.org --- fs/aio.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs') diff --git a/fs/aio.c b/fs/aio.c index 97bc62cbe2da..5f2e9c6c328e 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1111,6 +1111,12 @@ static long aio_read_events_ring(struct kioctx *ctx, tail = ring->tail; kunmap_atomic(ring); + /* + * Ensure that once we've read the current tail pointer, that + * we also see the events that were stored up to the tail. + */ + smp_rmb(); + pr_debug("h%u t%u m%u\n", head, tail, ctx->nr_events); if (head == tail) -- cgit v1.2.3